Interesting - but don't stand underneath it on a stormy day!
You've reminded me of a tree we spotted growing out from a wall of a derelict building, It was a stone building, old workhouse or hospital I think and the tree had taken root in a crack between the stones about half way up, maybe first or second floor.
I took a few shots at the time but they weren't any good as I didn't have a longer lens with me. Even more annoying is that we forgot the precise location! It was on a side road, small lane somewhere between Pett Level and Hastings iirc but we've been back several times and just can't find it again.
We keep looking though.